While Friday’s decision by the U.S. Court of Appeals in Washington left intact FAA guidance on restrictions over where recreational drones may fly, the ruling undercuts one of the agency’s primary means of ensuring that unmanned aircraft are operated safely. About 745,000 hobbyists have signed up since the FAA regulation was enacted in 2015. The agency estimates that 2.3 million drones will be sold this year for recreational use, plus 2.5 million for commercial operations.

Acting as his own lawyer, drone hobbyist John Taylor sued, contending the FAA didn’t have that power.

“Taylor does not think that the FAA had the statutory authority to issue the registration rule and require him to register,” U.S. Circuit Judge Brett Kavanaugh wrote for the unanimous three-judge panel. “Taylor is right.”

Drone registration was prompted by reports of the unmanned craft flying near traditional aircraft, including airliners at some of the largest U.S. airports. The registration system went into effect Dec. 21, 2015, as officials hurried to set it up before an expected spike in holiday sales.

Contrary to the mandate, though, was the FAA Modernization and Reform Act, passed by Congress in 2012 and signed by former President Barack Obama. The measure expressly barred the FAA from issuing rules governing model aircraft use, according to the court ruling.

The ruling doesn’t apply to the growing number of commercial drone operators, such as real estate photographers and cell-tower inspectors. It also won’t effect the plans of companies such as Amazon.com Inc. and Alphabet Inc. to create fleets of delivery drones”The number of unmanned aircraft has increased rapidly, creating significant concerns about the safety of the national airspace system, as well as the safety of persons and property on the ground,” the FAA argued in a 2016 brief in the case. “This is especially true given that many, if not most, owners of unmanned aircraft have no prior aviation experience and lack an understanding of the requirements for safe operation of their unmanned aircraft.”